This invention relates to a pneumatic-tube conveying installation for samples of fine material, comprising at least one sample despatch station for filling, closing and despatching sample carriers; a sample receiving station for receiving, emptying and returning the sample carriers to the sample despatch station; a feed tube connecting the sample despatch station to the sample receiving station; a blower designed to generate suction and pressure; and two non-return valves. The blower is associated with one station and the first non-return valve is arranged in that section of the feed tube which is situated between the two stations in the vicinity of the other station. The second non-return valve is arranged at that end of the feed tube which extends beyond such other station. The first non-return valve closes and the second non-return valve opens in the vacuum mode while the first non-return valve opens and the second non-return valve closes in the compressed-air mode.
A pneumatic-tube conveying installation of the type in question is generally laid out in such a way that the sample despatch station is set up in a suitable manufacturing part of a factory where a sampling unit, a sample mixer, a metering unit, etc. are also situated, while the sample receiving station is set up in a suitable place for processing the sample, particularly in a laboratory, so that random samples taken during production may be rapidly delivered to the sample processing department.
To this end, applicants have already developed a pneumatic-tube conveying installation of the above-mentioned type (DE-AS No. 27 22 865) which is distinguished from other known installations by a relatively simple tube system and by structural simplifications both in the sample despatch station and in the sample receiving station. In this pneumatic-tube conveying installation, the tube system may be formed by a single feed tube because the blower is designed to generate both suction and pressure and two correspondingly controllable non-return valves are provided in the feed tube. The various operations involving the sample carriers may be carried out at either station by means of a pivotal arm which may be turned into three different positions so that the three positions "despatch and receive", "open and close" and "fill" of the sample carriers are possible at the sample despatch station, while the three positions "receive and despatch", "open and close" and "empty and clean" are possible at the sample receiving station. The pivotal arm in question is driven by a Maltese-cross drive.